In an electrostatographic imaging process such as, for example, xerography, a xerographic plate containing a photoconductive insulating layer is imaged by uniformly electrostatically charging its surface followed by exposing it to a pattern of activating electromagnetic radiation such as light to selectively dissipate the charge in illuminated areas of the photoconductive member. This process forms an electrostatic latent image corresponding to the pattern of activating electromagnetic radiation. Alternatively, instead of latent image formation by uniformly charging a photoconductive layer and then exposing the layer to a light-and-shadow image, one may form the latent image by directly charging a dielectric layer in image configuration. The electrostatic latent image may then be developed with a developer composition containing charged marking particles. The charged particles will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder image may then be transferred to a support surface such as paper. The transferred image may be permanently affixed to the support surface as by heat. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.
To convert latent electrostatic images into visible images, a toner is generally used consisting of minute particles of a colored resin material which possesses definite triboelectric properties. Depending on the electrostatic charge the resin particles are either attracted and deposited on the charged areas of the latent image, or are repelled by the charged areas and deposited on the discharged areas. Such an operation is called the development of the latent electrostatic image.
In the electrostatographic process, liquid electrostatic developers are commonly used. Conventional commercial liquid developers comprise a dispersion of pigments in a liquid hydrocarbon. Once the electrostatic latent image is formed on an imaging member, it is transported through a bath of the liquid developer. When in contact with the liquid developer, the charged pigment particles in the liquid developer migrate to the electrostatic latent image and deposit thereon in conformance with the image. The imaging member may then be withdrawn from the liquid developer bath with the marking particles adhering to the electrostatic latent image in image configuration. A thin film of residual developer normally remains on the surface of the imaging member.
U.S. Pat. Nos. 4,762,764 to Ng et al. and 4,476,210 to Croucher et al. disclose a liquid developer comprising an amphipathic stabilizer polymer irreversibly anchored to a thermoplastic resin core of marking particles. The stabilizer has a soluble polymer backbone with an insoluble anchoring chain grafted onto the polymer backbone. The stabilizer may comprise an AB or ABA type block copolymer. The block copolymers may include siloxanes. The procedure for preparing the liquid developer comprises the steps of (1) preparation of the amphipathic stabilizer; (2) non-aqueous dispersion polymerization of the core monomer in the presence of the amphipathic stabilizer to provide stabilized particles; (3) dyeing of the non-aqueous dispersion particles; and (4) negatively charging the particles.
U.S. Pat. No. 3,579,451 to Sciambi discloses a stable, dry developer composition concentrate comprising silicone intermediate resin and a cross-linking promoting catalyst. The dry concentrate can be made into a liquid concentrate. The silicone intermediate resin component is a toluene- or xylene-soluble, lower alkyl and/or phenyl substituted, cross-linkable siloxane resin. The liquid developer composition concentrate is prepared by (1) heating a mixture of silicone intermediate resin and a cross-linking promoting catalyst suspended in an aromatic organic carrier liquid; (2) admixing the resin-catalyst mixture with an insoluble solid pigment; (3) milling the resin-catalyst mixture and pigment together in a grinding mill; (4) evaporating the milled materials to dryness; and (5) milling the dry concentrate with an organic carrier liquid to produce a liquid developer concentrate containing submicron-sized catalyst particles.
U.S. Pat. No. 4,737,432 to Tanaka et al. discloses a positively chargeable toner and a dry developer comprising positively chargeable fine silica powder. The silica powder may be treated to enhance hydrophobicity with another silane coupling agent or with an organic silicon compound, including such agents as hexamethyldisiloxane, 1,3-divinyltetramethyldi-siloxane, 1,3-diphenyltetramethyldisiloxane, and dimethyl-polysiloxane having 2 to 12 siloxane units per molecule and containing each on hydroxyl group bonded to Si at the terminal units.
U.S. Pat. Nos. 3,939,087 and 4,019,911, both to Vijayendran et al., disclose liquid toner compositions comprising a silane treated fumed silica. The silane treated fumed silica is treated with an organosilicon compound in which some of the bonds of a silane linkage are substituted by saturated or unsaturated hydrophobic organic groups.
U.S. Pat. No. 4,876,169 to Gruber et al. describes the use of siloxanes, in particular polydialkyl and polydimethyl siloxanes, incorporated in the backbone of a polymer resin in a dry toner or developer composition in conjunction with a release fluid additive which enables the toner to be free flowing and the toner particles not to agglomerate.
A need continues to exist for a liquid developer which provides good transfer efficiency, high resolution, dot range, print reproducibility, and print uniformity.